Project Summary With the traditional therapies for ovarian cancer (OC) that include surgery followed by cytotoxic chemotherapy patient survival is still extremely poor and 5-year survival rate is less than 30%. Therefore, new treatment strategies are needed to cure or improve dismal patient survival. Recent clinical and experimental evidence including ours indicate that the monocyte-macrophage axis (MMA) and tumor-associated macrophages (TAMs) play a significant role in tumor growth and progression by contributing to angiogenesis, invasion/metastasis, and drug resistance. We found OC patients with increased numbers of circulating monocytes and intratumoral TAMs have poor clinical outcomes and significantly shorter patient survival. Our studies also indicate that the tumor microenvironment and TAMs are attractive therapeutic targets in ovarian and other cancers and reduction of TAMs inhibits angiogenesis, invasion and metastasis, and drug resistance in ovarian cancer models. Overall data indicate that in contrast to the conventional drugs that target only tumor cells, targeting tumor microenvironment is required to achieve maximal anti-tumor efficacy. Also, lack of critical molecular targets for this purpose and together with a lack of effective delivery systems, biological barriers for drugs, including poor tissue-specific delivery, toxicity, and the inability to deliver high concentrations of therapeutics into tumor microenvironment, therapeutic strategies fail to cure OC. The use of siRNA bearing- nanoparticles targeted to the tumor and the microenvironment is a particularly attractive approach for targeting molecular targets, reprogramming the tumor microenvironment and development of the most effective therapeutic strategies for OC. To directly address these unmet needs we recently developed various nanoparticle (NP) platforms including, (1) long-acting, slow-release dual assembly NPs (DANPs); (2) serum resistant AXL-receptor binding-aptamers for development of targeted therapies in OC and validated each NP- based approach in multiple OC tumor models with robust and sustained target silencing and significant antitumor efficacy. In this study we will test the hypothesis that the blockade of the tumor and tumor microenvironment interactions by highly versatile NPs that encase therapeutic cargos will provide significant antitumor activity and enhance the efficacy of current regimens in OC. Thus we will determine mechanism of TAM regulation and determine the biological and therapeutic efficacy of targeting MMA/TAMs using highly targeted dual effect NPs in OC models as well as by applying mathematical models.